MULTIPATCH ANTENNA

Abstract: Multipatch antenna comprising radiating patches (2) positioned on a dielectric sheet (1) which patches (2) are capacitively fed by probes (7) ending in the dielectric sheet (1) near the patches (2). By positioning the probes (7) near selected edges of the radiating patches (2), a selected polarization direction of the radiation field can be realised. By positioning serveral probes (7) near a radiating patch (2), a radiation field with an adjustable polarization direction or a radiation field with an extremely low cross-polarization can be obtained.

Description: Multipatch antenna The invention relates to a multipatch antenna comprising an array of at least substantially equal radiating patches, positioned at one side of a dielectric sheet, a conductive ground plane positioned on the other side of the dielectric sheet and feeding means for energizing the patches. The invention furthermore relates to a phased array antenna comprising an array of K x L phased array elements and an array of K x L radiators for connection to the K x L phased array elements. Multipatch antennas are well-known in the art. They are relatively simple to produce and take up little space owing to their flat shape. In its most elementary embodiment, the multipatch antenna comprises a dielectric sheet, incorporating on one side an array of radiating patches and feeding means implemented as a microstrip network and on the other side a conductive ground plane, such as for instance presented in Fig. 1. Innumerable variations to this embodiment are possible, mostly aimed at reducing dielectric losses, increasing the antenna bandwidth, for providing the generated radiation pattern with a preselected or adjustable polarization or, for instance, for reducing cross-polarization. The present invention has for its object to realise a multipatch antenna that is easy to be constructed and has a large bandwidth. It is thereto characterised in that capacitive coupling means are provided to be incorporated between the feeding means and the patches. In case of the uncomplicated multipatch antenna presented in Fig. 1, the microstrip network is mounted on the side of the dielectric sheet which also comprises the patches. This is a suboptimal solution; the width of the microstrip network print tracks for example has to be chosen to be narrow so as to accommodate the patches. To obviate this drawback, the antenna according to the invention is further characterised in that the feeding means are positioned near the ground plane on the side facing away from the dielectric sheet. The ground plane is then provided with apertures at the location of the radiating patches to allow the passage of the capacitive coupling means. An exceptionally favourable embodiment of the invention is characterised in that the capacitive coupling means comprise conductive probes which are positioned at least substantially perpendicular to the dielectric sheet, each probe on one side connected to the feeding means and on the other side ending in the dielectric sheet, via the apertures, near a radiating patch. In addition to an antenna that is easy to be constructed and has a large bandwidth, this results in an antenna which enables a selection of the polarization direction of the radiation pattern. According to a first embodiment, the antenna is thereto characterised in that the probes end near selected edges of the radiating patches for generating a radiation pattern with a selected polarization direction. The feeding means will mostly be implemented as a transmission-line network, for instance a microstrip network mounted to a second dielectric sheet, which second dielectric sheet is mounted to the ground plane, the microstrip network being mounted on the side facing away from the ground plane. According to a second embodiment, the antenna is characterised in that two probes per radiating patch are provided, both ending near two opposed edges of the radiating patch. Energizing the two probes in opposite phases via the transmission line network results in a radiation pattern with a selected polarization direction and a very low cross-polarization. On account of its uncomplicated construction and the predictable behaviour of the radiating patches, the multipath antenna according to the invention can be conveniently used as a conformal array, for instance as a skin section of an aircraft. In this application, the patches are situated on a curved dielectric sheet which forms an integral part of the fuselage, the feeding means being mounted in the aircraft interior. As known in the art, the feeding means shall be arranged such as to allow for phase differences caused by the curvature of the antenna plane. Also the polarization behaviour of the antenna thus obtained can be excellently modelled due to the predictable behaviour of the radiating patches. According to a third embodiment, the feeding means comprise a second, separately feedable transmission line network. In a first application of this embodiment, the multipatch antenna is characterised in that for each radiating patch a first probe is provided for generating a radiation pattern with a first polarization direction and a second probe for generating a radiation pattern with a second polarization direction, which second polarization direction is at least substantially perpendicular to the first polarization direction. By connecting the first probe to the first transmission line network and the second probe to the second transmission line network and by subsequently feeding both networks in a suitable manner, an antenna with an adjustable polarization direction can be obtained. In a second application of this embodiment, the antenna is characterised in that for each radiating patch, a first pair of probes is provided for generating a radiation pattern with a first polarization direction and a second pair of probes for generating a radiation pattern with a second polarization direction being at least substantially perpendicular to the first polarization direction. The first transmission-line network is then arranged for feeding the first pair of probes with opposite phases and the second transmission-line network is arranged for feeding the second pair of probes with opposite phases. Thus, an antenna with an adjustable polarization direction and a very low cross-polarization is obtained. The present invention has furthermore for its object to provide an array of radiators that is easy to be constructed and that has a large bandwidth for connection to or to be integrated with K x L phased array elements, together constituting a phased array antenna system well- known in the art. To this end, the invention is is characterised in that the radiator array comprises an array of K x L at least substantially equal radiating patches, positioned on one side of a dielectric sheet and a conducting ground plane positioned on the other side of the dielectic sheet, the phased array elements being positioned near the conducting ground plane on the side facing away from the dielectric sheet. A favourable embodiment comprises capacitive coupling means for feeding the radiators positioned between the phased array elements and the radiating patches, the conducting ground plane being provided with apertures at the location of the radiating patches to allow the passage of the capacitive coupling means. An exceptionally favourable embodiment of the invention is characterised in that the capacitive coupling means comprise K x L conducting probes which are positioned at least substantially perpendicular to the dielectric sheet, each probe connected on one side with a phased array element and ending on the other side in the dielectric sheet near a radiating patch to be feeded. According to a first particular embodiment of the phased array antenna according to the invention, the probes end near selected edges of radiating patches for generating a radiation pattern with a selected polarization direction. According to a second particular embodiment of the phased array antenna according to the invention, the capacitive coupling means comprise 2 x K x L probes, each pair connected on one side with a phased array element and ending on the other side in the dielectric sheet near a radiating patch to be feeded. A first favourable application of this particular embodiment is characterised in that the phased array element is arranged for energizing a pair of probes with opposite phases, which probes end near opposed edges of the patch to be feeded. This yields a polarized radiation pattern with an extremely reduced cross-polarization. A second favourable application of this particular embodiment is characterised in that of each pair, a first probe is provided for generating a radiation pattern with a first polarization direction and a second probe for generating a radiation pattern with a second polarization direction which second polarization direction is at least substantially perpendicular to the first polarization direction. By controlling both probes in a suitable manner through the phased array element, an antenna with a controllable polarization direction is obtained. According to a third particular embodiment of the phased array antenna according to the invention, the coupling means comprise 4 x K x L conducting probes, each set of four connected on one side with a phased array element and ending on the other side in the dielectric sheet near a radiating patch to be feeded. A favourable application of this particular embodiment is characterised in that of each set of four probes, a first pair is provided for generating a radiation pattern with a first polarization direction and a second pair for generating a radiation pattern with a second polarization direction which second polarization direction is at least substantially perpendicular to the first polarization direction. By feeding each pair with opposite phases, an antenna with a controllable polarization direction and a reduced cross-polarization can be obtained. The invention will now be described in more detail with reference to the following figures, of which: Fig. 1 schematically represents a front view of an existing multipatch antenna and a microstrip-line network; Fig. 2 schematically represents a side view of an embodiment of the multipatch antenna according to the invention together with a microstrip-line network; Fig. 3 schematically represents the position of the probes for obtaining a radiation pattern with a horizontal polarization direction; Fig. 4 schematically represents the position of the probes for obtaining a radiation pattern with a vertical polarization direction; Fig. 5 schematically represents the position of the probes for obtaining a radiation pattern with a horizontal polarization direction and a reduced cross-polarization; Fig. 6 schematically represents the position of the probes for obtaining a radiation pattern with a vertical polarization direction and a reduced cross-polarization; Fig. 7 schematically represents a side view of an embodiment of the multipatch antenna according to the invention together with two microstrip-line networks; Fig. 8 schematically represents the position of the probes for obtaining a radiation pattern with an adjustable polarization direction; Fig. 9 schematically represents the position of the probes for obtaining a radiation pattern with an adjustable polarization direction and an extremely reduced cross-polarization; Fig. 10 schematically represents a side view of a multipatch antenna connected to an array of phased array elements; Fig. 11 schematically represents a side view of a multipatch antenna connected, via connectors, to an array of phased array elements. Fig. 1 shows a front view of an existing multipatch antenna, comprising a dielectric sheet 1 on which radiating patches 2(i,j) are mounted in a regular pattern. A δ transmission-line network 3 connects each radiation patch 2(i,j) to an input terminal 4 which, for instance via a coaxial connector not illustrated in the drawing, may be connected to a transmitter device or to a receiver device. Particularly the transmission-line network 3 has been represented in a very simplified manner, since various measures well-known in the art are required to prevent reflections and also to ensure an in-phase drive of all radiating patches 2(i,j). The dielectric sheet 1 is generally mounted to a metal plate not visible in the drawing and is made of a material having low dielectric losses. Although Fig. 1 shows a configuration of patches 2(i,j) arranged to lie in rows and columns, other configurations are also possible, such as for instance a configuration in which the odd-numbered rows are staggered half a column with respect to the even-numbered rows. This may prevent the occurrence of grating lobes. Fig. 2 shows a side view of an embodiment of a multipatch antenna according to the invention. On one side, the dielectric sheet 1 comprises a regular pattern of radiating patches 2(i,j) and on the other side it is provided with a metal plate 5. The transmission-line network 3, implemented as a microstrip-line network and provided with an input terminal 4, is, however, now mounted on a second dielectric sheet 6, which is also positioned on metal plate 5. This transmission-line network 3 may be identical to that shown in Fig. 1, although in view of the excess space, its implementation may also differ in detail, such in accordance with design criteria well-known in the art. Connection of the transmission-line network 3 to the radiating patches 2(i,j) is, according to the invention, effected by means of probes 7(i,j) which are connected on one side to the transmission-line network 3 and end on the other side in the dielectric sheet 1, near radiating patch 2(i.j). Thus transmission-line network 3 and radiating patch 2(i,j) are coupled capacitively. In order to allow the passage of probe 7(i,j), metal plate 5 is, where necessary, provided with holes 8, the diameters of which are selected in connection with the diameter of the probes 7(i,j) so as to minimize microwave radiation reflection. In the present embodiment the diameter of the probes 7(i,j) is 0.8 mm and the diameter of the holes is 1.8 mm. Dielectric sheet 6 is also provided with holes whose diameters correspond with the diameters of probes 7(i,j). These holes may be partially metal-plated to effect a reliable connection or to obtain improved microwave characteristics. In addition, the holes will often be surrounded by short-circuit pins to effect a proper coupling of the microwave energy in conducting probe 7(i,j). Dielectric sheet 1 is provided with blind holes, whose diameters correspond with the diameters of probes 7(i,j). In the present embodiment pertaining to an antenna operating in the 10 GHz frequency range, the thickness of the dielectric sheet 1 is 4.2 mm, probe 7(i,j) ending at 0.17 mm from radiating patch 2(i,j). Dielectric sheet 1 may for instance be made of Duroid, a material well-known in the art, which has a relative dielectric constant of 2.5. If so required, dielectric sheet 1 may comprise a sandwich consisting of two sheets, the first of which is drilled through to allow the passage of probes 7(i,j) and the second of which is not drilled for obtaining the specified distance between probes 7(i,j) and radiating patches 2(i,j). In another embodiment the diameter of the probe 7(i,j) is 1.27 mm and the diameter of the hole is 4.2 mm, the thickness of the dielectric sheet 1 is 6.61 mm and the probe 7(i,j) ends at 0.25 mm from radiating patch 2(i.j). The patch is rectangular with sides of 11.5 mm. The probe ends just underneath an edge of the patch, 1.15 mm away from a corner. This embodiment has at a centre frequency of 7 GHz a -lOdB bandwidth of 3.3 GHz. Instead of a microstrip network on a dielectric sheet, transmission-line network 3 may also consist of a sandwich of two dielectric sheets, clamped between two metal plates, the actual transmission line being positioned between the dielectric sheets. This construction, which is well-known in the art, is more complex, but produces a network with lower radiation losses. For some applications it is recommendable to cover the patches with an additional dielectric film. Apart from offering a protection against mechanical and chemical influences, this method may provide, at a favourably selected thickness and dielectric constant of the additional dielectric film, an additional increase of the antenna bandwidth. Fig. 3 schematically presents the position of a probe 7(i,j) with respect to the associated radiating patch 2(i,j) if an antenna with a horizontal polarization direction is required. By positioning the conducting probe near het centre of a vertical edge, the patch is excited such that energy is at least substantially radiated in a desired polarization direction. The application of a circular patch is also possible, the conducting probe shall then be positioned accordingly. As a rule, a rectangular patch is more advantageous for horizontal or vertical polarization. Similarly, Fig. 4 schematically represents the position of probe 7(i,j) with respect to the corresponding radiating patch 2(i,j) if an antenna with a vertical polarization direction is required. By positioning the conducting probe near the centre of a horizontal edge, the patch is excited such that energy is radiated at least substantially in a desired polarization direction. Fig. 5 schematically represents the position of probes 7(i,j) and 7'(i,j) with respect to the corresponding patch 2(i,j) if an antenna with a horizontal polarization direction and an extremely reduced cross-polarization is required. Both vertical edges of the radiating patch 2(i,j) are excited in opposite phases via transmission-line network 3, probe 7(i,j) and probe 7 ' (i,j) . Fig. 6 schematically represents the position of probes 7(i,j) and 7'(i,j) such that a vertical polarization direction with an extremely reduced cross-polarization can be realised analogously. Fig. 7 represents a side view of an embodiment of the multipatch antenna with a second transmission-line network 9 provided with an input terminal 4' , implemented as a microstrip network mounted on a second dielectric sheet 10 which is mounted on a second metal sheet 11. Transmission- line network 9 is provided with probes 14(i,j) which, via dielectric sheet 6 and metal plate 5, which is for that purpose provided with holes 13(i,j), end near radiating patches 2(i,j). This enables each radiating patch 2(i,j) to be provided with two probes 7(i,j), energized by transmission-line network 3 and two probes 14(i,j), energized by transmission-line network 9. Also this network 9 can be realised as strips clamped between two dielectric sheets and two metal plates or can be implemented in similar stripline technology. Fig. 8 schematically represents the position of probes 7(i,j) and 14(i,j) with respect to corresponding radiating patch 2(i,j) if an antenna with an adjustable polarization direction is required. A horizontal polarization direction can be obtained by feeding radiating patch 2(i,j) by transmission-line network 3 and probes 7(i,j) and a vertical polarization direction can be obtained by transmission-line network 9 and probes 14(i,j). As well- known in the art, any required polarization direction can then be realised by controlling the phase and amplitude of the microwave energy to be supplied to the transmission- line networks. Fig. 9 schematically represents the position of a first pair of probes 7(i,j) and 7 , (i,j) and a second pair of probes 14(i,j) and 14'(i,j) for obtaining a radiation pattern with an adjustable polarization direction and an extremely reduced cross-polarization. Probes 7(i,j) and 7 , (i,j) are fed through transmission-line network 3 in opposite phases and probes 14(i,j) and 14 , (i,j) are fed through transmission-line network 9 in opposite phases. Also in this case it is possible to realise any desired polarization direction by controlling, in phase and amplitude, the microwave energy supplied to the transmission-line networks, with the additional advantage that cross-polarization is limited by controlling the balanced steering of the pairs of probes. The multipatch antenna according to the invention is also preeminently suitable to be incorporated in a phased array antenna. Fig. 10 shows in cross section a dielectric sheet 1 provided with radiating patches 2(i,j), a metal plate 5 provided with holes 8(i,j) and probes 7(i,j). In this application, probes 7(i,j) are not fed by a transmission- line network, but from phased array elements 15(i,j) which are in turn fed in a way well-known in the art for obtaining a radiation pattern with adjustable beam parameters. Also the connection of a probe 7(i,j) to a electric circuit contained in the phased array element is well-known in the art. The present embodiment is preeminently suitable for creating subarrays of for instance 8 x 8 phased array elements connected to 8 x 8 radiating patches, each subarray then constituting a module in a phased array antenna system to be realised. Besides the extremely uncomplicated construction, the present embodiment has the advantage of said large bandwidth. In addition it is also possible to provide each phased array element with two probes. By feeding these probes at an adjustable phase and amplitude, an adustable polarization direction can be obtained, such in accordance with the description pertaining to Fig. 8. By feeding these probes in opposite phase, a polarization direction with a very low cross-polarization can be obtained, such in accordance with the description pertaining to Fig. 5 and Fig. 6. By means of phased array elements 15(i,j) which are suitable for the balanced feeding of two pairs of probes, as described with reference to Fig. 9, it is possible to analogously realise a phased array antenna with an adjustable polarization direction and a very low cross- polarization. Phased array elements 15(i,j) will usually be positioned in a backplane 16, via which control signals, supply voltages, transmit-receive signals and cooling are applied to the phased array elements. In this case the multipatch antenna shall be the final item in the assembly process, mounted from the front of the phased array antenna system. Fig. 11 shows a multipatch antenna according to the invention, suitable for front mounting. In this figure, metal plate 5 is provided with connectors 17(i,j), one for each probe 7(i / j) which is directly connected to the corresponding connector 17(i,j). By providing corresponding phased array element 15(i,j) with a counterpart 18(i,j) to connector 17(i,j), it is possible for the multipatch antenna to be the final item in the assembly process. In this respect it is advisable to select self-centring versions of connectors 17(i,j) and 18(i,j) and to divide the multipatch antenna into subarrays in order to reduce the forces acting during assembly or disassembly of the multipatch antenna.

Claims: Claims: 1. Multipatch antenna comprising an array of at least substantially equal radiating patches, positioned on one side of a dielectric sheet, a conductive ground plane positioned on the other side of the dielectric sheet, and feeding means for energizing the patches, characterised in that capacitive coupling means are incorporated between the feeding means and the patches. 2. Multipatch antenna as claimed in claim 1, characterised in that the feeding means are positioned near the ground plane on the side facing away from the dielectric sheet. 3. Multipatch antenna as claimed in claim 2, characterised in that the ground plane is provided with apertures at the location of the radiating patches to allow the passage of the capacitive coupling means. 4. Multipatch antenna as claimed in claim 3, characterised in that the capacitive coupling means comprise conducting probes which are positioned at least substantially perpendicular to the dielectric sheet, each probe on one side connected to the feeding means and on the other side ending in the dielectric sheet via the apertures, near a radiating patch. 5. Multipatch antenna as claimed in claim 4, characterised in that the probes end near selected edges of the radiating patches for generating a radiation pattern with a selected polarization direction. 6. Multipatch antenna as claimed in claim 5, characterised in that the feeding means comprise a first transmission- line network mounted to the ground plane on the side facing away from the dielectric sheet. 7. Multipatch antenna as claimed in claim 6, characterised in that the first transmission-line network comprises a microstrip network, mounted on a second dielectric sheet. 8. Multipatch antenna as claimed in claim 6 or 7, characterised in that for each radiating patch, two probes are provided, both ending near opposite edges of the radiating patch. 9. Multitpatch antenna as claimed in claim 8, characterised in that the transmission-line network is arranged for feeding the two probes in opposite phases. 10. Multipatch antenna as claimed in one of the above claims, characterised in that the antenna constitutes a conformal array on a curved ground plane. 11. Multipatch antenna as claimed in claim 6, characterised in that the feeding means comprise a second separately feedable transmission-line network. 12. Multipatch antenna as claimed in claim 11, characterised in that for each radiating patch, a first probe is provided for generating a radiation pattern with a first polarization direction and a second probe is provided for generating a second polarization direction which is at least substantially perpendicular to the first polarization direction. 13. Multipatch antenna as claimed in claim 12, characterised in that the first probe is connected to the first transmission-line network and the second probe is connected the second transmission-line network. 14. Multipatch antenna as claimed in claim 11, characterised in that for each radiating patch, a first pair of probes is provided for generating a radiation pattern with a first polarization direction and a second pair of probes is provided for generating a radiation pattern with a second polarization direction, the second polarization direction being at least substantially perpendicular to the first polarization direction. 15. Multipatch antenna as claimed in claim 14, characterised in that the first transmission-line network is suitable for feeding the first pair of probes with mutually opposite phases and the second transmission-line network is suitable for feeding the second pair of conducting probes with mutually opposite phases. 16. Phased array antenna, comprising an array of K x L phased array elements and an array of K x L radiators for connection to the K x L phased array elements, characterised in that the array of radiators comprises an array of K x L at least substantially equal radiating patches, positioned on one side of a dielectric sheet and a conductive ground plane, positioned on the other side of the dielectric sheet. 17. Phased array antenna as claimed in claim 16, characterised in that the phased array elements are positioned near the ground plane on the side facing away from the dielectric sheet. 18. Phased array antenna as claimed in claim 17, characterised in that capacitive coupling means are incorporated between the phased array elements and the radiating patches for energizing the radiators. 19. Phased array antenna as claimed in claim 18, characterised in that the ground plane is provided with apertures at the location of the radiating patches to allow the passage of the capacitive coupling means. 20. Phased array antenna as claimed in claim 19, characterised in that the capacitive coupling means comprise K x L conducting probes which are positioned at least substantially perpendicular to the dielectric sheet, each probe connected on one side with a phased array element and ending on the other side in the dielectric sheet near a radiating patch to be feeded. 21. Phased array antenna as claimed in claim 20, characterised in that the probes end near selected edges of the radiating patches in order to generate a radiation pattern with a selected polarization direction. 22. Phased array antenna as claimed in claim 19, characterised in that the capacitive coupling means comprise 2 x K x L probes, each pair connected on one side with a phased array element and ending on the other side in the dielectric sheet near a radiating patch to be feeded. 23. Phased array antenna as claimed in claim 22, characterised in that for each pair the probes end near opposed edges of the radiating patch to be feeded. 24. Phased array antenna as claimed in claim 23, characterised in that the phased array element is arranged for feeding the pair of probes in opposite phases. 25. Phased array antenna as claimed in claim 22, characterised in that of each pair, a first probe is provided for generating a radiation pattern with a first polarization direction and a second probe for generating a radiation pattern with a second polarization direction which second polarization direction is at least substantially perpendicular to the first polarization direction. 26. Phased array antenna as claimed in claim 19, characterised in that the capacitive coupling means comprise 4 x K x L conducting probes, each set of four probes being connected on one side with a phased array element and ending on the other side in the dielectric sheet near a patch to be energized. 27. Phased array antenna as claimed in claim 26, characterised in that of each set of four conducting probes, a first pair is provided for generating a radiation pattern with a first polarization direction and a second pair for generating a radiation pattern with a second polarization direction which second polarization direction is at least substantially perpendicular to the first polarization direction.

Inventors: POUWELS ARTHUR JOHANNES HENDRI, SMOLDERS ADRIANUS BERNARDUS, POUWELS, ARTHUR, JOHANNES, HENDRIKUS, SMOLDERS, ADRIANUS, BERNARDUS
Applicants: HOLLANDSE SIGNAALAPPARATEN BV, POUWELS ARTHUR JOHANNES HENDRI, SMOLDERS ADRIANUS BERNARDUS, STICHTING TECH WETENSCHAPP, HOLLANDSE SIGNAALAPPARATEN B.V., POUWELS, ARTHUR, JOHANNES, HENDRIKUS, SMOLDERS, ADRIANUS, BERNARDUS, STICHTING VOOR DE TECHNISCHE WETENSCHAPPEN
Application year: 1994
Main classification: H01Q9
IPC codes: H01Q9, H01Q21